Tubular Member Coupling and Lining Systems and Methods

ABSTRACT

For use in assembling a tubing string for a production well, a rigid pre-formed liner is configured for simple drop-in place installation at each tubing joint during assembly of the tubing string in to protect the inside of the tubing string from wear caused by operation of a sucker rod inside the same. At a threaded connection in the finished tubing string, where an externally threaded top end of a section of production tubing is engaged with an internally threaded bottom end of a box coupler or collar, the tubular portion of a respective liner hangs downward from a larger-diameter collar portion of the liner that sits atop the annular top end of the section of production tubing. The liner is installed by simply dropping its tubular portion into the section of tubing and then threading the box coupler onto the section tubing around the upper end of the liner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. 119(e) of Provisional Application Ser. No. 61/721,248, filed Nov. 1, 2012.

FIELD OF THE INVENTION

The present invention relates generally to well tube liners for use in well production, and more particularly to well tube liner inserts configured for easy drop-in installation during joining of tubing sections or joints for the purpose of providing a buffer between the tubing and a sucker rod deployed therein to operate downhole equipment.

BACKGROUND OF THE INVENTION

In pumping of fluids from a wellbore for production to the surface, a string of sucker rods connected end to end is used as a mechanical link between drive equipment at the surface and a downhole pump in the wellbore for driven operation thereof. Conventionally, sucker rods are typically each externally threaded at pin ends of the rod and are interconnected by internally threaded box couplings each threadingly receiving ends of adjacent rods in the string.

A common problem in such installations is that the sucker rod string does not extend entirely linearly in the wellbore, and accordingly box couplings between the rods, which are of larger outer diameter than the rods themselves and thus form the radially outermost extents of the string, will tend to bump or rub against the production tubing wall during the driven rotation of the rod string and thus cause significant wear to the production tubing. Accordingly, some solutions for preventing or limiting this wearing of the production tubing have been previously proposed to avoid the need for costly repair or replacement of damaged tubing.

One prior art solution has been to bond elastomeric materials to the hard outer surfaces of sucker rod couplers to reduce wear to the tubing, which is more difficult and costly to replace than a coupler. However, the coating may quickly wear away, requiring frequent replacement or recoating of sucker rod couplers.

U.S. Pat. Nos. 4,757,861 and 4,919,202 each teach a cylindrical shaft-like body that has a vaned cylindrical wheel of elastomeric material disposed and freely rotatable thereabout. The ends of the body are externally threaded in order to each engage a box coupling receiving a sucker rod therein from the opposite end thereof. The wheel is of greater outer diameter than the box couplers and accordingly forms the only contact between the drill string and the production tubing or well casing, and due to the relative rotation allowed between the wheel and the central body, moves very slowly, if at all, under the driven rotation of the drill string. This lack of significant rotation and the use of elastomeric material minimizes wear to the production tubing or well casing.

U.S. Pat. No. 5,511,619 teaches the application of wear-preventing elements on the tubing, instead of on the sucker rod string. An abrasion resistant polymer liner is installed by producing a liner having an outer diameter exceeding the inner diameter of the tubing, taking steps to reduce each liner's outer diameter to allow it to fit into the tube, then allowing the liner to attempt to return to its normal diameter, thereby frictionally engaging the outer surface of the liner to the inner surface of the tub to complete the installation.

U.S. Pat. No. 5,320,388 teaches a tubing liner for protection of the tubing against corrosive fluids, which of course requires that the entire internal surface of the tubing be covered by sections of liner. For each tube or tubing section, a first cylindrical liner piece is installed in the same way as described above, and a flange piece is then added to each end of the first piece. When the tubing sections are coupled together in a conventional manner using internally threaded collars or box couplers that engage the externally threaded pin ends of the tubing sections, the adjacent flanges between two tubing sections are clamped together, sealing them against one another and deforming them outward against the inner surface of the collar. The collection of liner pieces thus completely seal off the inner surfaces of the tubing from exposure to fluids flowing through the liner interior.

Installation of the prior art wear-prevention solutions can be time intensive, and thus inefficient. Applicant has developed a unique liner insert that is installed in a simple one-step process to protect against sucker rod wear of the tubing.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a well tubular coupling and lining system comprising:

a first tubular member having a first tubular member end with a first externally threaded portion adjacent the first tubular member end, said first externally threaded portion having an external diameter at the first tubular member end;

a second tubular member having a second tubular member end, internal threads engagable with the threaded portion of the first tubular member through the second tubular member end, and an internal surface spanning from the internal threads in a direction away from the second tubular member end;

a rigid pre-formed liner for insertion into the first tubing section through the first tubular member end, the pre-formed liner being a pre-formed unitary body comprising:

a tubular portion of length less than the first tubular member and of outer diameter smaller than an internal diameter of the first tubular member;

a collar portion integrally formed with the tubular portion at an end thereof and having an outer diameter that is larger than the internal diameter of the first tubular member and smaller than both the external diameter of the of the externally threaded portion of the first tubular member at the first tubular member end and an internal diameter of the second tubular member at the internal surface thereof; and

an internal passage extending through the tubular and collar portions from a first end of the body at the tubular portion thereof to an opposite second end of the body defined at the collar portion thereof.

Preferably the internal passage of the liner is tapered at the second end of the body to narrow toward the tubular portion thereof.

Preferably the internal passage of the liner is tapered at the first end of the body to narrow toward the collar portion thereof.

When the system is assembled for use, the first and second tubing sections are coupled together by engagement of the first externally threaded portion of the first tubular member with the internal threads of the second tubular member and the collar portion of the rigid liner is contained within the second tubular member past the first tubular member end.

When the system is in use, preferably the containment of the collar portion of the rigid liner alone acts to maintain the tubular portion of the rigid liner in a condition extending into the first tubular member.

When the system is in use, preferably the outer diameter of the tubular portion of the rigid liner is smaller than the internal diameter of the first tubular member and a clearance thus exists between an outer surface of the tubular portion of the rigid liner and an inner surface of the first tubular member.

When the system is in use, preferably the tubular portion of the rigid liner is maintained in a condition extending into the first tubular member independently of any contact between an outer surface of the rigid liner and an inner surface of the of the first tubular member.

When the system is in use, preferably the tubular portion of the rigid liner is in a non-sealed condition with of the second tubular member.

The collar portion of the rigid liner may be contained between the first tubular member end and a third tubular member end positioned within the second tubular member by engagement of a third tubular member into the second tubular member from an end thereof opposite the first tubular member, the third tubular member end jutting inward relative to the internal surface of the second tubular member.

The first tubular member may be a first tubing section and the second tubular member a collar-shaped coupler of shorter length than the first section of tubing, the system comprising a second tubing section that is longer than the collar-shaped coupler and comprises a second externally threaded portion, and the internal threads of the collar including threads engagable with the threaded portions of the first and second tubing sections from opposite ends of said collar.

In such instance, when the system is in use the first and second tubing sections are coupled together by engagement of the collar with the externally threaded portions of the tubing sections so that the collar portion of the rigid liner is contained between the coupled-together ends of the first and second tubing sections and the tubular portion of the rigid liner extends into the first tubing section from the collar portion.

According to a second aspect of the invention there is provided a well tubular coupling and lining method comprising:

providing first and second tubular members, the first tubular member having a first externally threaded portion and the second tubular member having internal threads engagable with the first externally threaded portion of the first tubular member;

providing a pre-formed rigid liner that has been pre-configured to have a tubular portion of outer diameter smaller than an internal diameter of the first tubular member and a collar portion integrally formed with the tubular portion at an end thereof with an outer diameter larger than the internal diameter of the first tubular member and smaller than the external diameter of the of the first externally threaded portion of the first tubular member;

without modifying the outer diameter of the tubular portion of the rigid liner, assembling the tubular members and the liner in a manner engaging the externally threaded portion of the first tubular member with the internal threads of the second tubular member and positioning and containing the rigid liner in a condition extending the tubular portion thereof into the first tubular member from the collar portion inside the second tubular member through an end of the first tubular member adjacent the first externally threaded portion;

whereby the rigid liner fluidly communicates the first and second tubular members via an internal passage extending through the rigid liner, and accommodates passage of a sucker rod string through the internal passage of the rigid liner to protect an inner surface of the first tubular member from contact with the sucker rod string.

Preferably the method includes connecting additional pairs of tubular members in a tubing string featuring the first and second tubular members in the same manner as the first and second tubing sections, whereby the rigid liners are suspended at respective tubular member couplings in the tubing string to protect a respective tubular member beneath each respective coupling.

The first tubular member may be a tubing section, and the second tubular member a collar, the system further comprising a second tubing section having a second externally threaded portion, the step of assembling the tubular members comprising inserting the tubular portion of the rigid liner into the first tubing section through the end thereof adjacent the externally threaded portion in order to seat a collar portion of the rigid liner against the end of the second tubing section, and coupling the first and second tubing sections together with the internally threaded collar.

Preferably a length of the tubular portion of each rigid liner is less than a length of the second tubular member.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:

FIG. 1 is a side elevational view of a well tubing liner insert of the present invention.

FIG. 2 is a bottom end view of the tubing liner insert.

FIG. 3 is a top end view of the tubing liner insert.

FIG. 4 is a cross-sectional view of the tubing liner insert as taken along line IV-IV of FIG. 1.

FIG. 5 is a perspective bottom view of the tubing liner insert.

FIG. 6 is a perspective top view of the tubing liner insert.

FIG. 7 is a partial elevational view of a pair of externally upset tubing sections coupled together by a collar, with the tubing sections and collar being partly sectioned to show a liner insert installed in the lower one of the tubing sections.

FIG. 8 is a partial elevational view of a pair of non-upset tubing sections coupled together by a collar, with the tubing sections and collar being cross-sectioned to show a liner insert installed in the lower one of the tubing sections.

FIG. 9 is a partially exploded elevational view of a liner insert installed in the lower one of a pair of tubing sections that couple directly together through matingly threaded box and pin ends of the sections without use of a collar.

FIG. 10 is a partial close up view of the tubing sections and liner insert of FIG. 9 in an assembled or made up state.

DETAILED DESCRIPTION

With reference to FIG. 7, the drawings show an embodiment of a liner insert 10 arranged to be placed within a section of a production tubing string 100 for a well so that a sucker rod string 102 to be extended downward through the tubing 100 for operation of a downhole pump in the wellbore is prevented from contacting the internal surface of the tubing string 100 at the location of the insert 10. The assembled conventional tubing string 100 features adjacent tube joints or sections 104, 106 situated one over the other in axial alignment and coupled together by means of an internally threaded collar or box coupler 108 that engages an externally threaded lower upset portion 110 of the upper tubing section 104 and an externally threaded upper upset end portion 112 of the lower tubing section 106. These conventional EUE (externally upset end) tubing sections are each of uniform inner diameter from end to end, and of uniform outer diameter between the opposite externally threaded upset end portions.

The liner insert 10 is configured for simple installation during assembly of the tubing string 100 by simply dropping it in place in the open upper end 114 of the lower tubing section 106 prior to coupling the tubing sections 104, 106 together by threaded fastening of the collar 108 onto the adjacent upset ends portions 110, 112 of the tubing sections 104, 106. The installed liner insert 10 sits in place at this coupling together of the tubing sections by the collar. An axial passage extends fully through the liner insert 10 to accommodate passage of the sucker rod string 102 therethrough, while the annular wall of the liner insert 10 provides a buffer between the sucker rod string 102 and the tubing wall surrounding the liner insert 10 to prevent the sucker rod string from causing wear or damage to the inner surface of the tubing wall. With a liner insert 10 positioned at each coupling of adjacent tube sections over a length of the tubing string 100, that length is thus protected from wear by the sucker rod string 102.

The liner insert 10 of the illustrated embodiment is a single unitary body of tubular shape having a lower portion 12 with an externally cylindrical shape and an upper portion 14 with a larger externally cylindrical shape of greater outer diameter than the lower portion 12. The upper portion 14 thus presents a collar extending radially outward beyond the outer periphery of the lower portion 14 at a shoulder 16 defined at this single-step change in the body's outer diameter. Where they meet, the integral upper and lower portions 14, 12 share a same internal diameter that is retained over nearly the full axial length of the body, making the internal passage 18 of the insert 10 a uniform cylindrical bore over most of its length. The only exceptions to this uniformity of the internal passage's diameter occur in the illustrated embodiment at the opposing upper and lower ends of the body 20, 22, where the internal passage 18 tapers in directions narrowing into the hollow interior passage 18 of the tubular body, as shown in the cross-section of FIG. 4 at 24 and 26.

Referring again to FIG. 7, the outer diameter of the lower portion 12 of the insert 10 is slightly smaller than the inner diameter of the lower tubing section 106, while the outer diameter of the upper portion 14 is larger than the inner diameter of the lower tubing section 106 but smaller than the outer diameter of the lower tubing section 106 defined at the open top end 114 thereof, as measured across thread grooves of the externally threaded upper upset portion of the lower tubing section (i.e. not including the crest-height of the thread in this “outer diameter” measurement). Accordingly, installation of the liner insert 10 in the lower tubing section 106 is achieved by lowering the insert's lower end 22 into the open top end 114 of the tubing section 106, and continuing to lower the insert liner 10 until the shoulder 16 between the upper and lower portions 14, 12 thereof becomes seated against the annular top end 114 of the lower tubing section 106. This seating of the upper collar portion 14 of the liner insert 10 atop the lower tubing section 106 acts to hang or suspend the lower tubular portion 12 down inside the lower tubing section 106 from the ledge formed the inward jutting of the upper end 114 of the lower tubing section 106 relative to an unobstructed stretch of the collar's inner surface above this upper end 114 of the lower tubing section 106.

The installation of the liner insert is completed by then coupling the tubing sections 104, 106 together in a conventional manner by threading the box coupling or collar 108 onto the externally threaded upset ends of the tubing section 104, 106 through relative rotation between the collar and the tubing sections. The resulting assembly is shown in FIG. 7, where the liner insert 10 is retained in its operational position depending into the lower tubing section 106 by trapping of the upper collar portion 14 of the liner insert 10 inside the collar 108 between the adjacent ends of the tubing sections 104, 106. That is, because each upset end among the tubing sections has the same inner and outer diameter as the other upset ends, the same relative sizing between the collar portion 14 of the insert and the top end 114 of the lower tubing section 106 exists between the collar portion 14 of the insert 10 and the bottom end 116 of the upper tubing section 104. Accordingly, the same way the outer diameter of the upper collar portion 14 of the insert 10 blocks the collar portion from sliding into the lower tubing section 106, so does it block the collar portion from sliding into the upper tubing section 104. As the length of the lower portion 12 of the insert 10 exceeds the axial distance between the top end 20 of the insert and the bottom end 116 of the upper tube section 104, full withdrawal of the lower tubular portion 13 outer of the lower tubing section 106 is thus prevented by the blocking of the collar portion 14 from moving upwardly past the bottom end of the upper tube section 104. The insert 10 is thus maintained in a position extending into the lower tubing section from the coupling provided between the two tubing sections by the engagement of the collar therewith.

A tubing string is completed by assembling further tubing sections atop the already assembled sections using respective additional collars, and preferably installing another insert at each coupling formed by such additional collars. The length of the lower section 12 of each insert 10 from the upper collar section 14 thereof to the bottom end 22 is preferably less than the length of tubing sections for which the insert is intended. This way, the insert 10 does not depend past the bottom end of the respective tubing section 106. If a longer insert is used, it cannot depend past the bottom end of the respective tubing section by a distance that would interfere with sufficient threading together of the tubing sections with the collar to provide a safe secure coupling thereof when accounting for the occupation of space between tubing sections in the collar by the collar portion 14 of the respective liner insert hanging into the tubing section immediately beneath that collar.

With an insert 10 installed at each joint in the tubing string, the sucker rod string 102 is prevented by contacting the interior surface of the tubing sections and collars at every point along the tubing string 100, as each liner insert prevents contact of the sucker rod string with the portion of the respective tubing section immediately surrounding that insert, and the length of the tubing sections and inserts is such that the axial distance along the tubing string between the inserts at adjacent couplings in the tubing string is short enough to prevent deflection of the sucker rod string to a degree that would reach the tubing string wall at locations between these adjacent liner inserts.

The function of preventing contact between the sucker rod string and the tubing wall does not require a fluid-tight sealed condition between the liner insert 10 and the tubing wall, and so unlike prior art tubing liners that are manipulated to initially fit loosely inside the respective tubing section and then expand in outer diameter after such placement to provide fluid tight sealing of the liner against the interior of the tubing wall, the insertion or dropping of each liner insert into the tubing section through its open end provides a simple installation process that requires only a single extra step beyond the standard steps of coupling together the tubing sections with the collar. Each insert is simply dropped in place into a respective tubing section, which is then coupled with another section in the conventional manner.

The liner inserts are thus manufactured to have pre-formed or pre-configured outer diameters at the upper collar portion and lower tubular portion that are sized to be smaller than the inner diameters of the tubing collar and tubing section respectively, as described herein above, to allow them to easily fit inside the tubing sections. Accordingly, no step of axially elongating the liner inserts to reduce their outer diameters to allow placement in the tubing, nor any other diameter-manipulating step, is required to install and use the liners, unlike the prior art liners mentioned herein above. Each liner insert is rigid, and maintains constant dimensions, including its diameters, throughout the installation process of inserting the liner insert in a respective tubing section and coupling that insert-equipped tubing section to a next tubing section above it. The containment of the collar portion of the rigid liner between the ends of the coupled together tubing sections acts to maintain the tubular portion of the rigid liner in a condition extending into the lower tubing section, and so the installation and operational position of the liner does not rely upon frictional contact of outer peripheral surfaces of the liner insert with surrounding internal surfaces of the tubing section or respective collar.

A prototype of the liner insert features a unitary body of ultra high molecular weight polyethylene (UHMW or UHMWPE) defining the integral lower portion and upper collar portion. Intended for use in EUE tubing sections of 3.5-inch outer diameter between the externally threaded upset ends of each section, the bottom end of the prototype insert features an outer diameter of 74.5 mm while the larger top end features an outer diameter 87.8 mm. The uniform inner diameter over most of the prototype's length is 61.0 mm, with the wall thickness narrowing to 3.5 mm at the upper end of the insert and to 3.3 mm at the lower end of the insert due to the tapered portions thereof, which act to prevent blocking or catching of the sucker rod string by the insert during lowering and raising of the sucker rod string in the tubing. The axial length of the upper collar portion is 33.7 mm from the shoulder to the upper end of the insert, while the lower portion extends 271.1 mm in the axial direction from the shoulder to the lower end of the insert. These prototype details are provided as examples only, and it will be appreciated that alternate materials or dimensions may be employed to produce an insert that installs and operates in the same manner. For example, differently sized inserts may be produced for use in tubing of different diameters or lengths and with sucker rods of varying diameter.

The insert sizing at the lower portion should be selected to provide a small enough outer diameter to fit easily into the tubing sections, but a large enough inner diameter to allow the sucker rod string to pass freely through the insert without excessive frictional restriction by the internal surface of the insert. Likewise, the upper portion should be sized with a small enough outer diameter to fit easily so as not to interfere with threaded engagement of the box or collar coupling of the tubing string with the tubing section in which the insert is placed, but a large enough inner diameter to again allow the sucker rod string to pass freely through the insert. As a result of this sizing, the outer peripheral surfaces of upper and lower portions of the insert are not in a fluid-tight sealed condition with the surrounding interior surface of the tubing section and collar, but slightly separated therefrom by a space, clearance or annulus.

As outlined above, FIG. 7 shows the insert in use in externally upset tubing where the outer diameter and wall thickness of each tubing section is greater at the externally threaded end portions of the section than at the uniform diameter central portion between these ends portions, and where a separate collar or coupling piece is used to interconnect adjacent tube sections in the string by engaging adjacent externally threaded ends of the tube sections at opposite ends of the internally threaded collar. However, FIGS. 8 to 10 demonstrate that use of liner inserts of the present invention is not limited to this particular type of tubing, and may be used in other tubing assemblies that likewise feature tubular members coupled together in a manner where the upper end of one tubular member effectively creates a ledge extending inward from the inner surface of another tubular member above, as this ledge can then be used in the same manner to hang a liner insert down into the lower of the two tubular members.

FIG. 8 shows non-upset tubing sections 104′, 106′ of a tubing string 100′ that are coupled together indirectly through use of an internally threaded collar or box coupling 108′ that engages threaded pin end portions 110′, 112′ of the tube sections 104′, 106′ from opposing ends of the collar 108′. The outer diameter of the collar portion 14 of the insert 10 is less than a minimum outer diameter of the lower tube section 106′, which occurs at the top end 114′ thereof due to the tapered configuration of the external threads at the upper pin end portion 112′. With the collar portion 14 smaller than this diameter between thread grooves at the top of the tubular section 106′, and likewise smaller than the minimum inner diameter between thread crests at the lengthwise center of the internally threaded coupling collar 108′, the insert 10 is suspended in the same manner as FIG. 7, with its collar portion 14 seated atop the lower tube section 106′ and its tubular portion 12 hanging from the collar portion 14 inside the lower tube section 106′ due to its smaller diameter being less than the uniform inner diameter of the lower tube section 106′. Again, because each end of each tubing section is the same size, the relative sizing of the collar portion relative to the top tube section 104′ is the same as to the lower tube section 106′, and the collar portion 14 of the insert 10 is accordingly retained inside the collar 108′ between the ends of the tube sections 104′, 106′ in the assembled tubing string.

FIGS. 9 and 10 illustrate how the insert may even be used in a tubing string where each tubing section features one internally threaded box-type end and one externally threaded pin-type end so that any two sections can be coupled together directly, without use of a separate collar or coupling, by threading the pin-end of one section into the box-end of the other. The insert 10 can be used when the illustrated tubing sections of this type are coupled together in pin-up orientations one over the other in axial alignment. The tapered threads of the externally threaded pin end 112″ at the top of the lower tubing section 106″ are configured to engage the tapered internal threads of the box end 110″ at the bottom of the upper tubing section 104″. As in FIGS. 7 and 8, the outer diameter of the collar portion 14 of the insert exceeds the inner diameter of the lower tubing section 106″ at the top end thereof, but is less than the outer diameter of the lower tubing section 106″ at the upper end 114″ thereof, as measured across thread grooves at this end. The outer diameter of the tubular portion 12 of the insert 10 is again smaller than the inner diameter of the lower tubing section 106″. Accordingly, the insert 10 again hangs partially within the lower tube section 106″ from its collar portion 14 seated atop the lower tube 106″.

In the insert applications shown in FIGS. 7 and 8, the outer diameter of the collar portion 14 of the insert is less than a minimum inner diameter of the collar used to couple the tubing sections together, and so the insert can be installed in the lower tube either before the collar is installed, or after the collar installed by dropping it therethrough. In FIGS. 9 and 10, where no separate collar or coupling is used, the minimum diameter of the upper tubing section 104″ that couples directly to the lower tubing section 106″ beneath it is less than the maximum outer diameter of the insert. Accordingly, the insert must be placed in the lower tubing section 106″ before threading of the next member of the tubing string at the top of the lower tubing section 106″. The insert 10 fits within the tubing string without interfering with the threaded coupling of the tubing sections 104″, 106″ because the inner diameter of the upper tubing section 104″ at a cylindrical interior surface 118 thereof spanning upward from the internal threading of the box portion 110′ is of great enough length in the axial direction, and great enough diameter thereacross, to accommodate the collar portion 14 of the insert 10 before the interior of the upper section 104″ reduces to a dimension less than the collar portion's outer diameter, as shown at 120. That is, the collar portion's outer diameter is less than the tubing's inner diameter at this span of interior tubing surface above the threaded bottom end of the upper tubing section, and the collar portion's axial length or height is less than the axial length or height of this span of the tubing section's interior.

The reduction in inner diameter 120 of the upper tubing section 104″ serves as a stop jutting inward from the interior surface 118 below it to block upward movement of the collar portion 14 of the insert 10 past it when the tubing section 104″, 106″ are coupled together. As the span of interior surface 118 from the internal threading of the box end portion to this stop is shorter than the tubular lower portion 12 of the insert 10, complete withdrawal of the insert from the lower tubular section 106″ is thus prevented in the same way as the upper tubing sections in FIGS. 7 and 8 block such withdrawal of the insert in order to maintain it in substantially concentric alignment inside the tubing.

The different applications shown in FIGS. 7 to 10 demonstrate how the insert can be used in different tubing make ups in which a lower tubular section is oriented to position an externally threaded male pin at its top end to engage an internally threaded female box end at the bottom of another tubular member, whether another tubing section or a shorter coupling collar, so long as this upper tubular member is of sufficient internal diameter immediately above its threaded engagement with the first tubular member for a sufficient distance to accommodate the outer diameter and height of the insert's collar portion without interfering with the necessary degree of threaded engagement between the tubular members to form a proper coupling thereof. In FIG. 7, this span is provided by a cylindrical inner surface extending fully between threaded end portions of the collar 108, while in FIG. 8 this span extends the full length of the collar, since even its minimum internal diameter is larger than the largest outer diameter of the insert. Likewise, the stop used to limit movement of the insert along the tube may vary, this function being provided in FIGS. 7 and 8 by the lower end of the upper tubing section disposed in the coupling collar, and being provided in FIG. 9 by a reduction in internal diameter of the upper tubing section coupled directly to the lower tubing section without a separate collar or coupling.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. Well tubular coupling and lining system comprising: a first tubular member having a first tubular member end with a first externally threaded portion adjacent the first tubular member end, said first externally threaded portion having an external diameter at the first tubular member end; a second tubular member having a second tubular member end, internal threads engagable with the threaded portion of the first tubular member through the second tubular member end, and an internal surface spanning from the internal threads in a direction away from the second tubular member end; a rigid pre-formed liner for insertion into the first tubing section through the first tubular member end, the pre-formed liner being a pre-formed unitary body comprising: a tubular portion of length less than the first tubular member and of outer diameter smaller than an internal diameter of the first tubular member; a collar portion integrally formed with the tubular portion at an end thereof and having an outer diameter that is larger than the internal diameter of the first tubular member and smaller than both the external diameter of the of the externally threaded portion of the first tubular member at the first tubular member end and an internal diameter of the second tubular member at the internal surface thereof; and an internal passage extending through the tubular and collar portions from a first end of the body at the tubular portion thereof to an opposite second end of the body defined at the collar portion thereof.
 2. The system of claim 1 wherein the internal passage of the liner is tapered at the second end of the body to narrow toward the tubular portion thereof.
 3. The system of claim 1 wherein the internal passage of the liner is tapered at the first end of the body to narrow toward the collar portion thereof.
 4. The system of claim 1 wherein the first and second tubing sections are coupled together by engagement of the first externally threaded portion of the first tubular member with the internal threads of the second tubular member and the collar portion of the rigid liner is contained within the second tubular member past the first tubular member end, containment of the collar portion of the rigid liner alone acting to maintain the tubular portion of the rigid liner in a condition extending into the first tubular member.
 5. The system of claim 1 wherein the first and second tubing sections are coupled together by engagement of the first externally threaded portion of the first tubular member with the internal threads of the second tubular member and the collar portion of the rigid liner is contained within the second tubular member past the first tubular member end, the outer diameter of the tubular portion of the rigid liner being smaller than the internal diameter of the first tubular member and a clearance thus existing between an outer surface of the tubular portion of the rigid liner and an inner surface of the first tubular member.
 6. The system of claim 1 wherein the first and second tubing sections are coupled together by engagement of the first externally threaded portion of the first tubular member with the internal threads of the second tubular member and the collar portion of the rigid liner is contained within the second tubular member past the first tubular member end, the tubular portion of the rigid liner being maintained in a condition extending into the first tubular member independently of any contact between an outer surface of the rigid liner and an inner surface of the of the first tubular member.
 7. The system of claim 1 wherein the first and second tubing sections are coupled together by engagement of the first externally threaded portion of the first tubular member with the internal threads of the second tubular member and the collar portion of the rigid liner is contained within the second tubular member past the first tubular member end, the tubular portion of the rigid liner being in a non-sealed condition with of the second tubular member.
 8. The system of claim 4 wherein the collar portion of the rigid liner is contained between the first tubular member end and a third tubular member end positioned within the second tubular member by engagement of a third tubular member into the second tubular member from an end thereof opposite the first tubular member, the third tubular member end jutting inward relative to the internal surface of the second tubular member.
 9. The system of claim 1 wherein the first tubular member is a first tubing section and the second tubular member is a collar-shaped coupler of shorter length than the first section of tubing, the system comprises a second tubing section that is longer than the collar-shaped coupler and comprises a second externally threaded portion, and the internal threads of the collar include threads engagable with the threaded portions of the first and second tubing sections from opposite ends of said collar.
 10. The system of claim 9 wherein the first and second tubing sections are coupled together by engagement of the collar with the externally threaded portions of the tubing sections so that the collar portion of the rigid liner is contained between the coupled-together ends of the first and second tubing sections and the tubular portion of the rigid liner extends into the first tubing section from the collar portion, containment of the collar portion of the rigid liner alone acting to maintain the tubular portion of the rigid liner in a condition extending into the first tubing section.
 11. The system of claim 9 wherein the first and second tubing sections are coupled together by engagement of the collar with the externally threaded portions of the tubing sections so that the collar portion of the rigid liner is contained between the coupled-together ends of the first and second tubing sections and the tubular portion of the rigid liner extends into the first tubing section from the collar portion, the outer diameter of the tubular portion of the rigid liner being smaller than the internal diameter of the first tubing section and a clearance thus existing between an outer surface of the tubular portion of the rigid liner and an inner surface of the first tubing section.
 12. The system of claim 9 wherein the first and second tubing sections are coupled together by engagement of the collar with the externally threaded portions of the tubing sections so that the collar portion of the rigid liner is contained between the coupled-together ends of the first and second tubing sections and the tubular portion of the rigid liner extends into the first tubing section from the collar portion, the tubular portion of the rigid liner being maintained in a condition extending into the first tubing section independently of any contact between an outer surface of the rigid liner and an inner surface of the of the first tubing section.
 13. The system of claim 9 wherein the first and second tubing sections are coupled together by engagement of the collar with the externally threaded portions of the tubing sections so that the collar portion of the rigid liner is contained between the coupled-together ends of the first and second tubing sections and the tubular portion of the rigid liner extends into the first tubing section from the collar portion, the tubular portion of the rigid liner being in a non-sealed condition with the first tubing section.
 14. Well tubular coupling and lining method comprising: providing first and second tubular members, the first tubular member having a first externally threaded portion and the second tubular member having internal threads engagable with the first externally threaded portion of the first tubular member; providing a pre-formed rigid liner that has been pre-configured to have a tubular portion of outer diameter smaller than an internal diameter of the first tubular member and a collar portion integrally formed with the tubular portion at an end thereof with an outer diameter larger than the internal diameter of the first tubular member and smaller than the external diameter of the of the first externally threaded portion of the first tubular member; without modifying the outer diameter of the tubular portion of the rigid liner, assembling the tubular members and the liner in a manner engaging the externally threaded portion of the first tubular member with the internal threads of the second tubular member and positioning and containing the rigid liner in a condition extending the tubular portion thereof into the first tubular member from the collar portion inside the second tubular member through an end of the first tubular member adjacent the first externally threaded portion; whereby the rigid liner fluidly communicates the first and second tubular members via an internal passage extending through the rigid liner, and accommodates passage of a sucker rod string through the internal passage of the rigid liner to protect an inner surface of the first tubular member from contact with the sucker rod string.
 15. The method of claim 14 comprising connecting additional pairs of tubular members in a tubing string featuring the first and second tubular members in the same manner as the first and second tubing sections, whereby the rigid liners are suspended at respective tubular member couplings in the tubing string to protect a respective tubular member beneath each respective coupling.
 16. The method of claim 14 wherein the first tubular member is a tubing section, the second tubular member is a collar, and the system further comprises a second tubing section having a second externally threaded portion, the step of assembling the tubular members comprising inserting the tubular portion of the rigid liner into the first tubing section through the end thereof adjacent the externally threaded portion in order to seat a collar portion of the rigid liner against the end of the second tubing section, and coupling the first and second tubing sections together with the internally threaded collar.
 17. The method of claim 16 comprising connecting additional pairs of tubing sections in a tubing string featuring the first and second tubing sections by using respective collars and rigid liners of a same type used for the first and second tubing sections, whereby the rigid liners are suspended at the respective collars in the tubing string to protect a respective tubing section beneath each respective collar.
 18. The method of claim 14 wherein a length of the tubular portion of the rigid liner is less than a length of the second tubular member.
 19. The method of claim 15 wherein a length of the tubular portion of each rigid liner is less than a length of the respective tubing section. 